Technical Field
The present invention relates to a thermostat device as a cooling device of an internal combustion engine (hereinafter referred to as an engine) that variably controls water temperature in a water-cooled temperature control system that variably controls the cooling water temperature of an engine for use in an automobile or the like, for example, and more particularly, to a mounting structure for a device housing of a thermo-element assembly thereof.
Background Art
For example, a thermostat device installed in a water-cooled system of an engine has a built-in thermal expansion unit (wax) that senses changes in temperature of the cooling water flowing through a circulatory flow path and expands and contracts accordingly. The thermostat device opens and closes a valve using volumetric changes attendant upon the expansion and contraction of the wax and functions to maintain the cooling water at a predetermined temperature.
Conventionally, as a thermostat device of this type, for example, one which, together with being disposed within a housing connected to a plurality of flow paths, has a piston fixedly mounted within the housing, a cylinder container that advances and retreats relative to the piston, wax provided within the housing that causes the cylinder container to advance and retreat due to volumetric changes attendant upon temperature changes, and a heat-emitting element provided within a piston casing that heats the wax when supplied with electricity, is known (see JP-2005-155831-A).
In a device with such a conventional structure, the heat-emitting element is composed of a thermally conductive extension member that penetrates into the interior of the casing from outside the piston casing, a heat-emitting portion formed within the part of the extension member inside the casing, and an electrode portion constructed of the part of the extension member outside the casing and electrically connected to the heat-emitting portion. A terminal that supplies voltage to the heat-emitting portion is contacted against the electrode part to electrically connect the heat-emitting portion with a voltage supply source. Then, by selectively causing the heat-emitting portion to emit heat, heat is conducted to the thermo-sensitive part wax and the cylinder container advances and retreats relative to the piston, such that the thermostat device is able to be caused to operate by electrical control regardless of the cooling water temperature.
With a construction such as this, because the terminal that supplies the voltage contacts the electrode of the extension member and is configured to be attachably detachable from the heat-emitting element, assembly and maintenance are easy. In addition, because the heat-emitting part of the heat-emitting element is formed inside the extension member and only the electrode part to which a voltage is applied is formed by the extension part, a highly durable heat-emitting element that does not break easily is able to be obtained. Moreover, because the heat-emitting element is provided within the piston casing, heat is able to be emitted substantially uniformly from the circumferential surface of the piston, and the thermal expansion unit is able to be heated effectively.
In a conventional electrically controlled thermostat device like that described above, the thermo-sensitive portion of the thermo-element assembly is normally exposed to the cooling water and thus is configured to be affected by the temperature of the cooling water, thereby enabling the device to function as a thermostat.
However, with a conventional device of this type, because it forcibly opens a main valve even at low temperatures in response to a requirement to defrost, for example, it is necessary to cover the thermo-sensitive portion of the thermo-element with a thermal insulation cover separate from the thermo-element, thereby rendering the thermo-sensitive portion less susceptible to the water temperature at low temperatures.
Although it is necessary to forcibly open the main valve, to reduce weight the cylinder container has thin walls. In that case, however, the wax is too easily affected by the cooling water temperature at low temperatures and does not easily heat up even with the use of a heater. In addition, compared to the case itself, which has thick walls, the cover that makes the case thin is lightweight.
In particular, this type of thermo-element thermo-sensitive portion is necessary in order to sense the temperature of the cooling water with wax, with the result that employing a thermal insulation structure involving a thermal insulation cover on this portion is not simply a matter of placing the thermal insulation on the thermo-sensitive portion but instead requires that some sort of special measures be taken. That is, it is necessary to satisfy two contradictory requirements: Namely, expanding and contracting the wax through the effects of heat from the temperature of the cooling water when necessary and securing the necessary operating conditions, while securing operating conditions that make use of the heat emitted by the heat-emitting element under required conditions when electrical control is necessary.
Moreover, in the above-described conventional device, in a case in which the thermal insulation cover is composed of only resin, the thermal insulation cover portion contacts a main valve spring and a bypass valve spring. The friction of contact between the main valve spring made of metal and the bypass valve spring made of metal, on the one hand, and the thermal insulation cover made of resin on the other damages or destroys the cover, with the possibility that pieces of resin get into the coolant circuit. To eliminate such a possibility, a metal washer or the like is placed between the contacting parts when the spring is contacted. But doing so raises a structural problem in the form of an increase in the number of components, and this point too must be given consideration.